Problem: Subtract.
Explanation: Let's use a number line to help us solve. $0$ $5$ $10$ $15$ $20$ Next, to subtract we move left $5$ on the number line. $0$ $5$ $10$ $15$ $20$ $13$ $- 5$ The jump ends at $8$. $0$ $5$ $10$ $15$ $20$ $13$ $- 5$ $\boxed{8}$ ${8}={13} - 5$